一个传感器板一个声学交通监控系统设计.pptx

Project GoalTo enable the study of a new technique for traffic monitoring using an acoustic array sensor network by:defining the system architecture of the sensor array board deriving the system specifications of the sensor array boarddesigning a PCB for the sensor array board and the interface to the wireless linkPresentation OutlineIntroduction to Traffic Surveillance NetworksIntroduction to Traffic Surveillance NetworksBackground on Passive Acoustic SensorsBackground on Passive Acoustic SensorsSystem ArchitectureSystem ArchitectureSystem SpecificationsSystem SpecificationsPart SelectionPart SelectionSchematic CaptureSchematic CapturePCB LayoutPCB LayoutFuture GoalsFuture GoalsTechnologies used for Rural Traffic SurveillanceNational Survey conducted in 2004 by ITSNational Survey conducted in 2004 by ITS1 1 found:found:26 states use Inductive Loop Detectors(ILD)26 states use Inductive Loop Detectors(ILD)21 states use Radar Detectors21 states use Radar Detectors 11 states use Video Image Detectors(VIDS)11 states use Video Image Detectors(VIDS)5 states use Acoustic Detectors5 states use Acoustic DetectorsVehicle info collected by the sensor networks include:Vehicle info collected by the sensor networks include:Traffic VolumeTraffic Volume Vehicle SpeedVehicle Speed Vehicle ClassificationVehicle Classification Travel TimeTravel Time Incident OccurrenceIncident Occurrence1 ITS or Intelligent Transportation System is a division of RITA which is part of the U.S.Department of Transportation(DOT).Inductive Loop Detectors(ILD)How it works:How it works:1 or more loops of wire are embedded under 1 or more loops of wire are embedded under the road&connected to a control box.the road&connected to a control box.When a vehicle passes over or rests on the When a vehicle passes over or rests on the loop,inductance is reduced showing a loop,inductance is reduced showing a vehicle is present.vehicle is present.BenefitsBenefits Established TechnologyEstablished Technology Not impacted by environmental conditions Not impacted by environmental conditions Accurate in detecting vehicle presenceAccurate in detecting vehicle presence Performs well in both high and low volume Performs well in both high and low volume traffictrafficDisadvantagesDisadvantages High Cost (up to$10k for initial costs)High Cost (up to$10k for initial costs)Invasive InstallationInvasive Installation Potential poor reliability due to improper Potential poor reliability due to improper installationinstallation Not viable for certain locations and road Not viable for certain locations and road conditionsconditions Unable to directly measure speed or directionUnable to directly measure speed or directionVideo Image Detection(VIDS)Employs machine vision technology to Employs machine vision technology to automatically analyze traffic data automatically analyze traffic data collected w/Closed Circuit Television collected w/Closed Circuit Television Systems(CCTV)Systems(CCTV)Benefits:Benefits:Rapid Incident detectionRapid Incident detection Wide area detection capabilities(multi-Wide area detection capabilities(multi-lane,multi-direction)lane,multi-direction)Vehicle classificationVehicle classification Estimates traffic queues and speedEstimates traffic queues and speed Installation does not require lane closuresInstallation does not require lane closures Can be integrated with other sensor Can be integrated with other sensor networksnetworksDisadvantages:Disadvantages:High Cost(initial cost$50k)High Cost(initial cost$50k)Higher Power than other sensor networksHigher Power than other sensor networks Light conditions can affect surveillanceLight conditions can affect surveillanceRadar-based Roadside SensorHow it works:How it works:Transmits radar pulsesTransmits radar pulses A portion of the energy is reflected or A portion of the energy is reflected or scattered from the vehicle and roadway scattered from the vehicle and roadway back toward the sensorback toward the sensor This energy is received and interpreted.This energy is received and interpreted.BenefitsBenefits Low PowerLow Power Most accurate technology for detecting Most accurate technology for detecting speed speed Traffic Count accuracyTraffic Count accuracy Easy installationEasy installation Low costLow costDisadvantagesDisadvantages Accuracy can be affected by weather Accuracy can be affected by weather conditions(hail,snow,rain)conditions(hail,snow,rain)Directional Detection is poorDirectional Detection is poor Interference could occur with other RF Interference could occur with other RF devicesdevicesPassive Acoustic SensorsPassive Road-side Sensor that Passive Road-side Sensor that receives sound waves from passing receives sound waves from passing vehicles.vehicles.Benefits:Benefits:Low PowerLow Power Low CostLow Cost Easy to InstallEasy to Install Directional and Multi-lane DetectionDirectional and Multi-lane Detection Accurately measures traffic countAccurately measures traffic countDisadvantages:Disadvantages:Accuracy affected by environment Accuracy affected by environment factorsfactors Speed measurements are not as Speed measurements are not as accurate as other methodsaccurate as other methodsSummary of Traffic Surveillance Technologies Employed Today:Radar and Acoustic sensors are the least expensive to deploy and are the Radar and Acoustic sensors are the least expensive to deploy and are the lowest power.lowest power.VIDS collect the most information and the data processing possibilties are VIDS collect the most information and the data processing possibilties are endless.endless.Acoustic sensors are the least accurate,but the technology is relatively new.Acoustic sensors are the least accurate,but the technology is relatively new.Acoustic sensors for traffic monitoring has room for improvement:Acoustic sensors for traffic monitoring has room for improvement:Improve accuracy Improve accuracy Ability to detect idle trafficAbility to detect idle traffic Intelligently process data(Vehicle Classification,Incident Detection)Intelligently process data(Vehicle Classification,Incident Detection)TechnologyTraffic Volume(Moving)Traffic Volume(Stopped)Vehicle SpeedVehicle ClassificationIncident DetectionPowerCostILDsAACDCBCRadarAAACCBAVIDsBBBAACCPassive AcousticBCBBCAACodeA Excellent;B Fair;C-Poor;D Nonexistent;U Unknown Acoustic Array SensorResearch has shown that Research has shown that using arrays of acoustic using arrays of acoustic sensors narrows the detection sensors narrows the detection zone for improved SNR&zone for improved SNR&better accuracybetter accuracyFor this project the following For this project the following configuration will be evaluated:configuration will be evaluated:4 microphone arrays per sensor:4 microphone arrays per sensor:2 arrays form a pair parallel to 2 arrays form a pair parallel to the roadthe road2 arrays for a pair orthogonal to 2 arrays for a pair orthogonal to the roadthe roadEach array contains 12 Each array contains 12 microphonesmicrophones Sensors to be deployed road-Sensors to be deployed road-side about 10m above the road.side about 10m above the road.Sensor Network System DetailsSound detected by each Sound detected by each element in a single array element in a single array will be summed together will be summed together and amplified.and amplified.4 analog outputs will be 4 analog outputs will be digitized separately and digitized separately and processed.processed.Processed signals will be Processed signals will be transmitted to a gateway transmitted to a gateway node within the wireless node within the wireless sensor network.sensor network.Signal Processing:Parallel PairA vehicle moves across the detection zone(D2 to D1):A vehicle moves across the detection zone(D2 to D1):As a vehicle approaches,sound reaches D2 earlier than As a vehicle approaches,sound reaches D2 earlier than D1.The time delta will be negative(D1.The time delta will be negative(0).0).When a vehicle is at the center of the detection zone,When a vehicle is at the center of the detection zone,=0.=0.As a vehicle exits the detection zone,As a vehicle exits the detection zone,will be positive.will be positive.The rate of change or slope across the detection zone The rate of change or slope across the detection zone corresponds to the vehicle speed.corresponds to the vehicle speed.To extract the time delay from the actual signals,the To extract the time delay from the actual signals,the cross correlation of D1 and D2 is calculated:cross correlation of D1 and D2 is calculated:Signal Processing:Orthogonal PairA vehicle moves across the A vehicle moves across the detection zone:detection zone:As the vehicle approaches,sound As the vehicle approaches,sound will reach D1 earlier than D2.The will reach D1 earlier than D2.The time difference will be positive and time difference will be positive and increasing(increasing(0).0).When the vehicle is at the center When the vehicle is at the center of the detection zone,of the detection zone,will peak.will peak.As the vehicle exits the detection As the vehicle exits the detection zone,zone,will be positive and will be positive and decreasing.decreasing.The sound map for vehicles in The sound map for vehicles in lanes closer to the sensor lanes closer to the sensor(smaller y)will have smaller(smaller y)will have smaller peaks than those in lanes peaks than those in lanes further from sensor.further from sensor.System Architecture2 Boards to form complete system:2 Boards to form complete system:Sensor Board Sensor Board Microphone ArraysMicrophone ArraysSumming StageSumming StageAmplification StageAmplification Stage System BoardSystem BoardAnalog-to-Digital ConverterAnalog-to-Digital ConverterProcessorProcessorRF Transceiver(ISM band of 2.4GHz)RF Transceiver(ISM band of 2.4GHz)eZ430-RF2480 Demo Kit from TI eZ430-RF2480 Demo Kit from TI chosen for System Boardchosen for System Board USB-based wireless demo toolUSB-based wireless demo tool MSP430F2274 Mixed-Signal MSP430F2274 Mixed-Signal MicrocontrollerMicrocontroller CC2480 2.4GHz ZigBee network CC2480 2.4GHz ZigBee network processorprocessor 2.4GHz Antenna2.4GHz AntennaSensor Board ArchitectureFor initial prototype,1 sensor board per array to allow for For initial prototype,1 sensor board per array to allow for array spacing experimentationarray spacing experimentationMajority of System Gain implemented on Sensor board Majority of System Gain implemented on Sensor board to maximize SNR.to maximize SNR.Clipping Circuit and Anti-Aliasing Filter may be needed to Clipping Circuit and Anti-Aliasing Filter may be needed to condition signal for ADC.condition signal for ADC.System Board ArchitectureMSP430 Mixed-Signal MicrocontrollerMSP430 Mixed-Signal Microcontroller AUX Op-Amps can provide extra gain if neededAUX Op-Amps can provide extra gain if needed On-chip 10-bit ADC can multiplex in 4 analog channels for On-chip 10-bit ADC can multiplex in 4 analog channels for digitizingdigitizing CPU can be programmed to compute cross-correlation functionsCPU can be programmed to compute cross-correlation functionsCC2480 ZigBee Processor to transmit data to gateway CC2480 ZigBee Processor to transmit data to gateway node to main control center over 2.4GHz ISM bandnode to main control center over 2.4GHz ISM bandDetermining Sensor Board SpecsPower Supply RequirementsMaximum Voltage Output SwingElement SpacingSumming Stage ConfigurationSystem GainAnti-Aliasing FilterPower Supply Requirements2 Specifications need to be determined:2 Specifications need to be determined:Supply VoltagesSupply Voltages Maximum CurrentMaximum CurrentSensor Board needs to be portable solution Sensor Board needs to be portable solution Low powerLow power Battery operatedBattery operatedReuse Battery Board included with eZ430-Reuse Battery Board included with eZ430-RF2480 Demo Kit:RF2480 Demo Kit:2 AAA Batteries in series:3V supply2 AAA Batteries in series:3V supply Capacity of AAAs:900-1155mA/hCapacity of AAAs:900-1155mA/hMaximum Voltage Output SwingNeeds to be limited to Input Range of ADC.Needs to be limited to Input Range of ADC.Depending of ADC front-end architecture,over voltage on inputs Depending of ADC front-end architecture,over voltage on inputs can cause conversion errors and in some cases damage the can cause conversion errors and in some cases damage the ADC.ADC.10-bit ADC integrated on the MSP430 will be used.10-bit ADC integrated on the MSP430 will be used.ADC input range is programmable from Vcc to Vss.ADC input range is programmable from Vcc to Vss.For this project,ADC will be programmed to accept an input For this project,ADC will be programmed to accept an input range of 3V to 0V.range of 3V to 0V.No Clipping Circuit needed on Sensor BoardNo Clipping Circuit needed on Sensor Board Amplifiers on Sensor board will not produce a voltage higher Amplifiers on Sensor board will not produce a voltage higher than its supply voltagethan its supply voltage ADC on the MSP430 clips any signals greater than the ADC on the MSP430 clips any signals greater than the programmable upper input range limit.programmable upper input range limit.Benefits from using the same power source solution!Benefits from using the same power source solution!Element SpacingSpacing b/t array elements will be Spacing b/t array elements will be chosen to achieve the desired chosen to achieve the desired detection angle.detection angle.Desired Detection Angle:Desired Detection Angle:Sensor board mounted 10m above road Sensor board mounted 10m above road(z=10m)(z=10m)Desired detection zone is 2.5m in any Desired detection zone is 2.5m in any direction at road level.direction at road level.Detection Angle can be calculated:Detection Angle can be calculated:Experiment to Determine Element SpacingSeveral 3x4 element arrays Several 3x4 element arrays bread-boarded w/summing bread-boarded w/summing stage:stage:Array 1:1.75cm x 1.75cmArray 1:1.75cm x 1.75cm Array 2:2cm x 2cmArray 2:2cm x 2cm Array 3:2.5cm x 2.5cmArray 3:2.5cm x 2.5cmDetection Angle measured by Detection Angle measured by moving a 4kHz sound source moving a 4kHz sound source across the array from a fixed across the array from a fixed distance.distance.V Vpk-pkpk-pk measured at summer measured at summer output with Oscilloscopeoutput with OscilloscopeResults of Element Spacing ExperimentsSumming Stage ConfigurationOriginal Design used 1 op-amp to sum all 12 elementsOriginal Design used 1 op-amp to sum all 12 elementsNew Design sums the elements in 2 stages:New Design sums the elements in 2 stages:First stage sums the 3 rows of 4 elements separatelyFirst stage sums the 3 rows of 4 elements separately Second stage sums the 3 outputs of the 1Second stage sums the 3 outputs of the 1stst stage stageNew Design allows for more gain without large RNew Design allows for more gain without large R Improved Rise/Fall Times(Improved Rise/Fall Times(=RC)=RC)Increased Bandwidth less Gain per stage(fIncreased Bandwidth